1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device suitable for a ferroelectric memory.
2. Description of the Related Art
In the process of forming a ferroelectric capacitor used for a ferroelectric memory and the like, an anneal is required for recovering damages of a ferroelectric film.
FIG. 10A to FIG. 10C are sectional views showing a first example (a first prior art) of the conventional method for manufacturing a semiconductor device having a ferroelectric capacitor in order of processes. In the first prior art, as shown in FIG. 10A, a ferroelectric capacitor composing of a lower electrode 103, a PZT film 104, and an upper electrode 105 are formed on an interlayer insulating film 101 by patterning and the like.
Next, an anneal for recovering the capacitor is conducted in an oxygen atmosphere. In this anneal, as shown in FIG. 10B, since an oxygen deficit in the PZT film 104 is made up for by oxygen supplied from an exposed part (a side part) of the PZT film 104, a characteristic of the capacitor is recovered. However, at the same time of this process, Pb in the PZT film 104 is diffused outside and evaporated, so that the characteristic of the capacitor deteriorates.
Subsequently, as shown in FIG. 10C, an alumina protective film 106 is formed for preventing the deterioration caused by infiltration of hydrogen and/or moisture in a subsequent wiring process (a process for forming wiring), further, an interlayer insulating film 102 and a wiring (not shown) and the like are formed.
In the semiconductor device thus fabricated, the portion of which characteristic deteriorates with the decrease of Pb in the PZT film 104 remains as it is. Therefore, the sufficient characteristic can not be obtained.
On one hand, a method for forming a comparatively thin capacitor protective film after the ferroelectric capacitor is formed is introduced. FIG. 11A to FIG. 11C are sectional views showing a second example (a second prior art) of the conventional method for manufacturing a semiconductor device having a ferroelectric capacitor in order of processes. In the second prior art, as shown in FIG. 11A, a ferroelectric capacitor composing of a lower electrode 103, a PZT film 104 and an upper electrode 105 are formed on an interlayer insulating film 101 by patterning and the like, after that, a comparatively thin alumina protective film 106 is formed.
Next, an anneal for recovering the capacitor is conducted in an oxygen atmosphere. As shown in FIG. 11B, since an oxygen deficit in the PZT film 104 is made up for by oxygen supplied from an exposed part (a side surface) of the PZT film 104, a characteristic of the capacitor is recovered. Differently from the first prior art, the diffusion of Pb to outside does not occur.
Subsequently, as shown in FIG. 11C, an interlayer insulation film 102 and a wiring (not shown) and the like are formed. In the second prior art, however, on occasion of forming the interlayer insulation film 102, or on occasion of forming other interlayer insulation films, or on the other occasions and the like, hydrogen and/or moisture are infiltrated into the PZT film 104 through the alumina protective film 106, so that the sufficient characteristic can not be obtained. That is why the thickness of the alumina protective film 106 is insufficient.
On the other hand, a method for forming a thick capacitor protective film after the ferroelectric capacitor is formed is adoptable. FIG. 12A to FIG. 12C are sectional views showing a third example (a third prior art) of the conventional method for manufacturing a semiconductor device having a ferroelectric capacitor in order of processes. In the third prior art, as shown in FIG. 12A, a ferroelectric capacitor composing of a lower electrode 103, a PZT film 104 and an upper electrode 105 are formed on an interlayer insulating film 101 by pattering and the like, after that, an alumina protective film 106 whereof thickness is sufficient for protecting the capacitor is formed.
After that, an anneal for recovering the capacitor in an oxygen atmosphere. In this anneal, as shown in FIG. 12B, differently from the first prior art, a diffusion of Pb to outside does not occur. However, the supply of oxygen from an exposed part (a side surface) of the PZT film is also interrupted, as a result, an oxygen deficit is not made up for.
Subsequently, as shown in FIG. 12C, an interlayer insulating film 102 is formed, further, a wiring (not shown) and the like are formed.
In the semiconductor device thus fabricated, the oxygen deficit in the PZT film 104 remains as it is. Therefore, the sufficient characteristic can not be obtained.
The protective film such as an alumina film covering a ferroelectric capacitor is deposited in such processes as the deterioration of the ferroelectric film is small. The deterioration is caused by hydrogen and/or moisture reducing the ferroelectric film in a deposition environment. Especially, in CVD method in which a wafer often suffered from heat, the deterioration of the ferroelectric film is conspicuous.
As for the processes for depositing the alumina film as the protective film without deteriorating the ferroelectric film, a sputtering process using an alumina target in an atmosphere of Ar gas, and a reactive sputtering process using an aluminum target in an atmosphere including oxygen can be cited. In these processes, since a reducing environment does not exist, the protective film can be deposited without deteriorating the ferroelectric film.
However, as a microfabrication art is progressed, a side wall of the capacitor becomes steep, so that a sufficient coverage can not be obtained by the sputtering process. In order to obtain the sufficient coverage, employing the CVD method is required. However, in the case of employing the CVD method as described above, the ferroelectric film is easy to deteriorate.
Meanwhile, a method for depositing the alumina film employing an ALD (Atomic layer deposition) method is described in a patent document (Japanese Patent Application Laid-open No. 2002-100742). In this method, an atomic layer deposition alumina is mainly used as the protective film. In general, when forming the atomic layer deposition alumina, a good deal of moisture exists in the deposition atmosphere, so that the moisture is easy to be absorbed in the depositing process. Thus, the moisture makes the ferroelectric film deteriorate by the sequential heat treatment or the like. In short, in ALD method, water is often used as an oxidant of TMA (tri-methyl-aluminum) as a material. Since this moisture becomes a source of generating hydrogen, the ferroelectric film deteriorates. In the method described in the patent document, after a very thin first protective film (1 nm to 1.5 nm) is deposited, an anneal is performed in order to remove the moisture absorbed into a ferroelectric film on forming the first protective film. Then, a second protective film opposed to the deterioration factor in the sequential wiring process is formed comparatively thick.
However, in the way described in the patent document, since the first protective film is extremely thin, oxygen can be supplied to the PZT film by the heat treatment but evaporation of Pb in the PZT film can not be suppressed sufficiently.
Furthermore, in a conventional method, after the ferroelectric capacitor is formed, the interlayer insulating film 102 made of Si is formed. Then a W-plug for a bulk contact is formed, further, an insulating film into which nitrogen is mixed is formed for preventing a oxidation of the W-plug, after that, a contact hole reaching to an upper electrode and a contact hole reaching to a lower electrode are formed. And a heat treatment at 500° C. or higher is conducted for recovering damage (process deterioration) of the capacitor with oxygen supplied from the contact holes.
However, in the conventional method, the efficiency of recovery obtained by the anneal is not sufficient.
Besides, after an alumina protective film is formed, an interlayer insulating film and a wiring and so on are formed. When the interlayer insulating film is formed, damages often arise. FIG. 13A to FIG. 13J are sectional views of a conventional method for manufacturing a semiconductor device having a ferroelectric capacitor, showing mainly a method for forming an interlayer insulating film in order of processes.
First, after a field effect transistor is formed on a semiconductor substrate, an interlayer insulating film 101 is formed as shown in FIG. 13A.
Next, as shown in FIG. 13B, a lower electrode film 103 and the PZT film 104 are formed sequentially on the interlayer insulating film 101. Then a crystallization anneal is performed to the PZT film 104. After that, an upper electrode film 105 is formed on the PZT film 104.
Subsequently, as shown in FIG. 13C, by patterning the upper electrode film 105 with an etching process employed, an upper electrode is formed. Next, oxygen anneal for recovering damages caused by the patterning with the etching process employed is performed. Further, by patterning the PZT film 4, a capacity insulating film is formed. An Al2O3 film 151 is formed, as a protective film, on the whole surface by a sputtering process. Next, by patterning the Al2O3 film 151 and the lower electrode film 103, a lower electrode is formed. After that, an Al2O3 film 152 is formed, as a protective film, on the whole surface by the sputtering process.
Next, as shown in FIG. 13D, an interlayer insulating film 154 is formed on the whole surface, and a planarization of the interlayer insulating film 154 is conducted by a CMP (Chemical Mechanical Polishing) method. The thickness of the interlayer insulating film 154 is approximately 1.5 μm.
Subsequently, as shown in FIG. 13E, a hole reaching to a high concentration diffused layer (not shown) of the transistor is formed through the interlayer insulating film 154 and the like. After that, by forming a Ti film and a TiN film sequentially in the hole, a barrier metal film (not shown) is formed. Further, a W-film is embedded in the hole employing a CVD (Chemical Vapor Deposition) method. And by executing the planarization of the W-film employing the CMP method, a W-plug 155 is formed.
Next, as shown in FIG. 13F, a SiON film 156 is formed for preventing the oxidation of the W-plug.
Next, as shown in FIG. 13G, a hole reaching to the upper electrode film 105 and a hole reaching to the lower electrode film 103 are formed through the SiON film 156 and the like.
After that, as shown in FIG. 13H, the oxygen anneal is performed for recovering damages. In this oxygen anneal, oxygen reaches to the PZT film 104 via the upper electrode 105, at the same time, oxygen reaches there via the interlayer insulating film 154, the Al2O3 films 152 and 151 from the neighborhood of interface between the upper electrode film 105 and the PZT film 104.
Subsequently, as shown in FIG. 13I, the SiON film 156 is removed through the whole surface by an etch-back process, so that the surface of the W-plug 155 is exposed.
Next, as shown in FIG. 13J, under the condition that a part of the surface of the upper electrode film 105, a part of the surface of the lower electrode film 103 and the surface of the W-plug 155 are exposed, an Al film is formed. By pattering the Al film, an Al wiring 157 is formed.
Furthermore, an interlayer insulating film, a contact plug, wirings under the second layer from the bottom and the like are formed. Then, a cover film composing of, for example, a TEOS oxidized film and a SiN film is formed to complete a ferroelectric memory having the ferroelectric capacitor.
However, when the semiconductor device is fabricated in the way described above, hydrogen and/or moisture easily reaches to the PZt film 104 on forming the interlayer insulating film 154, as a result, a characteristic deteriorates.